1. Field of the Invention
The present invention relates to a thin-film magnetic head manufacturing method and apparatus for precisely lapping thin-film magnetic heads for use in magnetic disk devices and the like.
2. Description of the Related Art
In manufacturing thin-film magnetic heads, in general, thin layers constituting thin-film magnetic elements, such as insulating layers, magnetic layers, and conductive layers, are stacked in order on a substrate made of Al2O3xe2x80x94TiC (alumina titanium carbide) by sputtering, and the thin layers are worked by photolithography or ion milling as required.
In order to manufacture thin-film magnetic heads, plural thin-film magnetic elements 1 are formed in plural rows on a substrate 2, as shown in FIG. 5 (FIG. 5 shows only some of the thin-film magnetic elements 1). A thin-film magnetic element 1 is a so-called xe2x80x9cMR (magnetoresistive)/inductive combined magnetic headxe2x80x9d in which an MR magnetic head having a magnetoresistive sensor for reading recorded information and an inductive magnetic head for writing are combined. The thin-film magnetic elements 1 are electrically connected by electrodes 4 connected thereto. The substrate 2 is cut along the dotted lines to yield a slider bar as shown in FIG. 6.
In manufacturing a thin-film magnetic head, the height of the magnetoresistive sensor of the MR magnetic head in the thin-film magnetic element 1 must be adjusted to a predetermined value. The MR height is adjusted by lapping an ABS (air-bearing surface) 3a shown in FIG. 6 while using some of a plurality of magnetoresistive sensors as monitor elements, and measuring DC resistance values (DCR values) between the electrode layers connected to both ends of the magnetoresistive sensors.
By lapping the ABS 3a until the DCR value fall into the finish tolerances, the height of the magnetoresistive sensors (MR height) can be set at an appropriate value. After the MR height is adjusted, the slider bar 3 is cut along the dotted lines shown in FIG. 6 into individual thin-film magnetic heads. Individual substrates cut from the slider bar 3 serve as sliders. The ABS 3a of the slider faces a recording medium and receives a levitating force when the recording medium moves.
Lapping for adjusting the MR height is performed by using, for example, a lapping plate 21 shown in FIG. 8. The slider bar 3 shown in FIG. 6 is placed so that the ABS 3a thereof is in contact with the surface of the lapping plate 21. The lapping plate 21 is rotationally driven to lap the ABS 3a of the slider bar 3.
FIGS. 9A and 9B are flowcharts showing the process of lapping for adjusting the MR height.
Lapping is performed in two stages, rough lapping (FIG. 9A) with a lapping fluid applied on the upper surface of the lapping plate 21, and finish lapping (FIG. 9B) with a lubricant applied on the lapping plate 21 as necessary.
In rough lapping, as shown in FIG. 9A, lapping is continued while the DCR values of the monitor elements are being monitored, and is completed when the DCR values fall into a predetermined DCR range.
In finish lapping shown in FIG. 9B, lapping is similarly performed while the DCR values of the monitor elements are being monitored, and it is completed when the DCR values fall into the finish tolerance range, which means that the MR heights also falls into the finish tolerance range.
In a conventional lapping method, as shown in FIGS. 9A and 9B, however, a level difference is likely to remain between the ABS 3a of the slider bar 3 and the thin-film magnetic element 1 in a completed thin-film magnetic head.
FIGS. 11A and 11B are side views of the slider bar 3 and the thin-film magnetic element 1, respectively, before lapping is started, and during or after lapping. When the thin-film magnetic element 1 is formed (the process shown in FIG. 5), a cover layer 5 is formed to cover the thin-film magnetic element 1. This cover layer 5 is made of Al2O3 or SiO2.
In rough lapping, as described with reference to FIG. 9A, the lapping fluid contains fine particles, and the ABS 3a is lapped therewith.
The thin-film magnetic element 1 primarily made of Al2O3, NiFe (permalloy), or the like is lapped at a higher rate than the slider bar 3 made of Al2O3xe2x80x94TiC (alumina titanium carbide) or the like. Therefore, as shown in FIG. 11B, a level difference is likely to be formed between the ABS 3a of the slider bar 3 and a surface 1a of the thin-film magnetic element 1 opposing the recording medium in rough lapping.
In particular, in rough lapping with the lapping fluid applied on the surface of the lapping plate 21, the opposing surface 1a of the thin-film magnetic element 1 is likely to be lapped at a high rate by the fine particles in the lapping fluid, which increases the amount of level difference (recession). Hereinafter, the amount of level difference (recession) is represented by the letter xe2x80x9cRxe2x80x9d. The recession R is zero when the opposing surface 1a of the thin-film magnetic element 1 is flush with the ABS 3a of the slider bar 3, and the direction in which the recession R increases is designated the xe2x80x9cpositive (+) directionxe2x80x9d.
Since rough lapping, as shown in FIG. 9A, is performed while monitoring only the DCR values of the magnetoresistive sensors, when the DCR values fall into a predetermined range, that is, when the heights of the magnetoresistive sensors (MR height) fall into a predetermined range, it is impossible to determine the extent to which the ABS 3a of the slider bar 3 has been lapped. For this reason, even when the opposing surface 1a of the thin-film magnetic element 1 has been sufficiently lapped and the MR height values are within the predetermined range, the ABS 3a of the slider bar 3 has not been sufficiently lapped and a substantial recession R is produced in the positive direction.
In the subsequent finish lapping process, the opposing surface 1a of the thin-film magnetic element 1 is lapped at a higher rate than the ABS 3a of the slider bar 3. Therefore, in a case in which a substantial recession R is produced during rough lapping, that is, when a great difference remains in the levels between the ABS 3a of the slider bar 3 and the opposing surface 1a of the thin-film magnetic element 1, if finish lapping is performed while monitoring only the DCR values, as shown in FIG. 9B, a substantial recession R remains when the DCR values of the thin-film magnetic element 1 falls into the finish height tolerances.
That is, although too large a recession R remains at the completion of rough lapping, and the ABS 3a of the slider bar 3 is not lapped to sufficiently reduce the recession R due to a short finish lapping time, finish lapping is completed.
Because of the need to cope with recent increases in density of recording media, thin-film magnetic heads have been required to minimize the distance between the opposing surface of the thin-film magnetic element and a recording medium in a driving state to reduce spacing loss as much as possible. If a substantial recession is produced in such a thin-film magnetic head as described above, the spacing loss increases, and this impairs writing/reading characteristics.
In general, the lapping plate 21 is rotated at approximately 100 rpm for the purpose of lapping. Conventionally, the lapping plate 21 is controlled by trapezoidal driving so that the power applied to a motor for driving the lapping plate 21 is switched from the driving state to a stop state at the completion of finish lapping. When the lapping plate 21 rotating at a high speed is rapidly stopped at the completion of finish lapping, flaws are produced on the ABS 3a of the slider bar 3 and the opposing surface 1a of the thin-film magnetic element 1.
The flaws on the ABS 3a of the slider bar 3 remain unchanged on an ABS of the slider, floating characteristics on the recording medium becomes unstable, or flaws may be produced on the surface of the recording medium.
In order to solve the above problems in the conventional art, an object of the present invention is to provide a thin-film magnetic head manufacturing method and apparatus in which lapping is performed so as to minimize the recession between an ABS of a slider bar and a surface of a thin-film magnetic element opposing a recording medium.
Another object of the present invention is to provide a thin-film magnetic head manufacturing method and apparatus in which flaws are prevented from being produced on an ABS of a slider bar at the completion of finish lapping.
According to one aspect of the present invention, there is provided a thin-film magnetic head manufacturing method for forming a thin-film magnetic element including a magnetoresistive sensor by stacking thin-film layers, such as an insulating layer, a magnetic layer, and a conductive layer, on a substrate, and for adjusting the MR height by lapping the substrate and the thin-film magnetic element in the height direction while measuring the resistance value of the magnetoresistive sensor, wherein lapping is continued until the lapping time exceeds a predetermined time and the resistance value or the MR height converted from the resistance value falls into the finish tolerances.
According to the present invention, lapping is not performed with reference only to the resistance value or the height value converted from the resistance value, which is different from that in the conventional art, and lapping is monitored until the lapping time exceeds a predetermined time. When the lapping time exceeds the predetermined time and the resistance value or the height converted from the resistance value falls into the finish tolerances, lapping is completed. By continuing the lapping for longer than the predetermined time while monitoring the resistance, as described above, it is possible to sufficiently lap the ABS of the substrate (slider bar) having a low lapping rate, to minimize the recession between the ABS and the surface of the thin-film magnetic element, and to make the recession zero.
According to another embodiment of the present invention, there is provided a thin-film magnetic head manufacturing method for forming a thin-film magnetic element including a magnetoresistive sensor by stacking thin-film layers, such as an insulating layer, a magnetic layer, and a conductive layer, on a substrate, and for adjusting the MR height by lapping the substrate and the thin-film magnetic element in the height direction while measuring the resistance value of the magnetoresistive sensor, wherein the rotation rate of a lapping plate in a lapping machine used for lapping is switched to a lower rate at least once to complete lapping when the resistance value or the MR height converted from the resistance value falls below a reference value.
When the lapping comes close to an end, that is, when the resistance value or the MR height converted from the resistance value falls below a reference value, the rotation rate of the lapping plate in the lapping machine is switched to a lower rate at least once, and the rotation of the lapping plate is stopped to complete lapping. This makes it possible to reduce flaws in the ABS of the slider and the surface of the thin-film magnetic element, to improve the floating characteristics of the thin-film magnetic head, and to prevent a magnetic head from producing flaws on a recording medium.
It is possible to adopt both the aspect of the invention of switching the rotation rate of the lapping plate in the lapping machine used for lapping at least once when the resistance value or the MR height converted from the resistance value falls below a reference value, and the aspect of the invention of continuing lapping until the lapping time exceeds a predetermined time and the resistance or the MR height converted from the resistance value falls into the finish tolerances.
Preferably, lapping includes the two stages of rough lapping and finish lapping, and the predetermined lapping time corresponds to the time that has elapsed from the beginning of finish lapping.
Lapping may include the two stages of rough lapping and finish lapping, and the rotation rate may be switched during finish lapping.
Rough lapping, which places more importance on lapping speed than on lapping accuracy, is performed at a high speed until the MR height approaches a target value, and it is switched to finish lapping, which places importance on lapping accuracy, when the MR height comes close to the target value. This can increase the lapping accuracy and shortens the overall lapping time.
In these two stages, rough lapping and finish lapping, by monitoring whether the finish lapping time is longer than a predetermined time, it is possible to prevent, for example, insufficient lapping of the substrate, which will result in a large recession, when the recession in rough lapping is too large, that is, when the thin-film magnetic element has been subjected to a greater degree of lapping than the substrate, and lapping is completed in a short time of subsequent finish lapping.
The aspect of the invention in which the finish lapping time has been monitored to determine if its has exceeded the predetermined time may be carried out by monitoring the time elapsed from the beginning of lapping in a method having a single lapping stage instead of the two stages of rough lapping and finish lapping.
Similarly, the rotation rate may be switched in the method having a single lapping stage.
Preferably, the predetermined lapping time is set to be, for example, more than two minutes, more preferably, more than three minutes.
Preferably, the rotation rate of the lapping plate is, for example, 70 to 100 rpm before switching, and is 5 to 20 rpm after switching.
In the present invention, the recession from the thin-film magnetic element to the surface of the substrate opposing the recording medium may be measured after the completion of finish lapping, and the lapping conditions of the next lapping may be changed so that the recession, or the MR height or resistance of the magnetoresistive sensor, is appropriate.
The time from the beginning of finish lapping to the completion of finish lapping may be measured, and the lapping conditions of the next lapping may be changed so that the measured lapping time is within a predetermined range.
The lapping conditions may include, for example, the amount of adjustment of the MR height during rough lapping and the timing for feeding a lubricant during finish lapping.
Preferably, a plurality of different lapping conditions, such as the MR height in rough lapping and the timing for feeding a lubricant in finish lapping, are ranked, listed in a table, stored, and selected from the table by selecting the rank.
When the lapping conditions necessary for lapping are collected, ranked according to the MR heights, listed in a table, and stored according to the lapping machine, the operator can set the lapping conditions (MR height, the lubricant feeding time) for the next lapping simply by selecting the rank in the lapping conditions in the table based on data from the results of the previous lapping (recession, MR height or resistance, finish lapping time). Therefore, it is possible to shorten the time taken for setting, to reduce setting errors, and to improve the quality and yield of thin-film magnetic heads.
In the present invention, lapping may be performed with reference to the resistance, or the MR height may be converted from the resistance so that it is determined base on the converted value whether the lapping amount of the finishing value is appropriate.
That is, when the resistance of the magnetoresistive sensors is measured in the above methods, lapping may be performed while monitoring the resistance as it falls into a predetermined range or the finish tolerances, whereas the lapping state may be monitored using the MR height converted from the resistance.
According to another aspect of the present invention, there is provided a manufacturing apparatus for carrying out the above-described thin-film magnetic element manufacturing method, including a holding means for holding a thin-film magnetic head in which a thin-film magnetic element including a magnetoresistive sensor is formed on a substrate; a lapping machine for lapping the substrate and the thin-film magnetic element in the thin-film magnetic head held by the holding means; a resistance measuring means for measuring the resistance of the magnetoresistive sensor during lapping; and a control means for monitoring the resistance measured by the resistance measuring means or the MR height converted from the resistance, determining whether the lapping time exceeds a predetermined time, and controlling the lapping machine until the lapping time exceeds the predetermined time and the resistance or the MR height falls into finish tolerances.
According to another aspect of the present invention, there is provided a manufacturing apparatus for carrying out the above-described thin-film magnetic element manufacturing method, including a holding means for holding a thin-film magnetic head in which a thin-film magnetic element including a magnetoresistive sensor is formed on a substrate; a lapping machine for lapping the substrate and the thin-film magnetic element in the thin-film magnetic head held by the holding means; a resistance measuring means for measuring the resistance of the magnetoresistive sensor during lapping; a speed changing means for changing the rotation rate of a lapping plate in the lapping machine; and a control means for monitoring the resistance measured by the resistance measuring means or the MR height converted from the resistance, and controlling the speed changing means so that the rotation rate of the lapping plate in the lapping machine is switched to a lower rate at least once when the resistance or the MR height converted from the resistance falls below a reference value.
According to a further aspect of the present invention, there is provided a manufacturing apparatus for carrying out the above-described thin-film magnetic element manufacturing method, including a holding means for holding a thin-film magnetic head in which a thin-film magnetic element including a magnetoresistive sensor is formed on a substrate; a lapping machine for lapping the substrate and the thin-film magnetic element in the thin-film magnetic head held by the holding means; a resistance measuring means for measuring the resistance of the magnetoresistive sensor during lapping; a speed changing means for changing the rotation rate of a lapping plate in the lapping machine; and a control means for monitoring the resistance measured by the resistance measuring means or the MR height converted from the resistance, determining whether the lapping time exceeds a predetermined time, controlling the lapping machine until the lapping time exceeds the predetermined time and the resistance or the MR height falls into finish tolerances, and controlling the speed changing means so that the rotation rate of the lapping plate in the lapping machine is switched to a lower rate at least once when the resistance or the MR height converted from the resistance falls below a reference value.
Preferably, the lapping machine performs lapping in two stages of rough lapping and finish lapping and the control means measures the lapping time from the beginning of finish lapping, or the lapping machine performs lapping in two stages of rough lapping and finish lapping and is controlled by the control means so that the rotation rate of the lapping plate is switched during finish lapping.
Preferably, the apparatus further includes a memory device for storing a table containing a plurality of ranked lapping conditions, and the control means sets, as a lapping condition for the next lapping, the lapping condition read from the table according to the finishing result of finish lapping.
Further objects, features, and advantages of the present invention will be apparent from the following description of the preferred embodiments with reference to the attached drawings.